Effects of biological, economic and management factors on tuna and billfish stock status

Published source details Pons M., Branch T.A., Melnychuk M.C., Jensen O.P., Brodziak J., Fromentin J.M., Harley S.J., Haynie A.C., Kell L.T., Maunder M.N., Parma A.M., Restrepo V.R., Sharma R., Ahrens R. & Hilborn R. (2017) Effects of biological, economic and management factors on tuna and billfish stock status. Fish and Fisheries, 18, 1-21.
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This study is summarised as evidence for the following.

	Action	Category
	Introduce an overall catch limit (quota cap or total allowable catch) by fishery or fleet Action Link

Introduce an overall catch limit (quota cap or total allowable catch) by fishery or fleet

A replicated, controlled study in 2004–2014 of marine areas worldwide (Pons et al. 2016) found that previously depleted stocks of tunas Scombridae and billfishes (swordfish Xiphiidae, marlins and sailfish Istiophoridae) managed under catch limits (total allowable catches) resulted in faster increases of biomass and lower fishing mortality compared to stocks with at least one type of other management control or no management measures. For both tuna and billfish stocks, annual average rates of change of biomass were higher and increasing, and rates of fishing mortality were higher and decreasing, for stocks currently managed under total allowable catch quotas (8 stocks) than stocks with some management measures including minimum size regulations or seasonal closures (28 stocks) or no measures (12 stocks: data presented graphically). In addition, the number of years since quota implementation was the most important for increasing biomass compared to the other control types, but measures such as minimum size regulations and seasonal closures were more important in reducing fishing mortality (see paper for data). Data were obtained from stock assessment outputs compiled from a global stock assessment database (see original paper for details); for 40 stocks of 13 species, seven species of major commercial tunas and six species of billfishes from at least 48 stocks defined globally. Data for management variables were compiled from information available on the websites and reports of different management organisations and through personal communication with their staff.

(Summarised by: Natasha Taylor)